Method and system related to electrosurgical procedures

ABSTRACT

Electrosurgical procedures. At least some of the example methods that include: supplying energy to an active electrode of an electrosurgical wand, the supplying energy to the active electrode by an electrosurgical controller; monitoring an electrical parameter associated with the energy; and determining, based on the electrical parameter, the presence of a wand condition of the electrosurgical wand, the wand condition being at least one selected from the group consisting of: a surface area of the active electrode is less than a predetermined threshold surface area; the surface area of the active electrode is approaching the predetermined threshold surface area; and that the electrosurgical wand is affected by a blockage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/339,621 filed Jul. 24, 2014, the disclosure of which is incorporatedby reference in its entirety.

BACKGROUND

Electrosurgical systems are used by physicians to remove severaldifferent tissue types. For example, procedures involving the knee orshoulder may remove portions of cartilage, meniscus, and free floatingand/or trapped tissue. In some cases, the removal may be a very slightremoval, such as tissue sculpting, and in other cases the moreaggressive removal of tissue is used. Removing each different tissuetype, and/or aggressiveness, may represent a different amount of appliedenergy.

Electrosurgical wands used with electrosurgical systems inelectrosurgical procedures have a limited useful life. Any advance thatmakes determining when an electrosurgical wand has reached the end ofits useful life and/or fluid flow through the wand has been at leastpartially blocked during an electrosurgical procedure would enablesurgeons to plan more effectively and/or take corrective action.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments, reference will nowbe made to the accompanying drawings in which:

FIG. 1 shows an electrosurgical system in accordance with at least someembodiments;

FIG. 2 shows an elevation view of an electrosurgical wand in accordancewith at least some embodiments;

FIG. 3 shows a cross-sectional elevation view of an electrosurgical wandin accordance with at least some embodiments;

FIG. 4 shows both an elevation view an active electrode and aperspective view of the distal end of a wand (including the activeelectrode) in accordance with at least some embodiments;

FIG. 5 shows a block diagram of an electrosurgical controller inaccordance with at least some embodiments; and

FIG. 6 (comprising FIGS. 6A and 6B) shows a flow diagram in accordancewith at least some embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies that design and manufacture electrosurgicalsystems may refer to a component by different names. This document doesnot intend to distinguish between components that differ in name but notfunction.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection or through anindirect connection via other devices and connections.

Reference to a singular item includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said” and “the”include plural references unless the context clearly dictates otherwise.It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement serves as antecedent basis foruse of such exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Lastly, it is to be appreciated that unless definedotherwise, all technical and scientific terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs.

“Ablation” shall mean removal of tissue based on tissue interaction witha plasma.

“Mode of ablation” shall refer to one or more characteristics of anablation. Lack of ablation (i.e., a lack of plasma) shall not beconsidered a “mode of ablation.” A mode which performs coagulation shallnot be considered a “mode of ablation.”

“Active electrode” shall mean an electrode of an electrosurgical wandwhich produces an electrically-induced tissue-altering effect whenbrought into contact with, or close proximity to, a tissue targeted fortreatment.

“Return electrode” shall mean an electrode of an electrosurgical wandwhich serves to provide a current flow path for electrical charges withrespect to an active electrode, and/or an electrode of an electricalsurgical wand which does not itself produce an electrically-inducedtissue-altering effect on tissue targeted for treatment.

“Electric motor” shall include alternating current (AC) motors, directcurrent (DC) motors, as well as stepper motors.

“Controlling flow of fluid” shall mean controlling a volume flow rate.Control of applied pressure to maintain a set point pressure (e.g.,suction pressure) independent of volume flow rate of liquid caused bythe applied pressure shall not be considered “controlling flow offluid.” However, varying applied pressure to maintain a set point volumeflow rate of liquid shall be considered “controlling flow of fluid”.

“Energy range” shall refer to a lower limit energy, upper limit energy,and all the intervening energies between the lower limit and the upperlimit. A first energy range and a second energy range may overlap (e.g.,the lower limit of the second energy range may be an intervening energyin the first energy range), but so long as at least a portion of eachenergy range is mutually exclusive, the two energy ranges shall beconsidered distinct for purposes of the specification and claims.

“Energy setpoint” shall refer to a specific energy that falls within anenergy range.

“Impedance” shall mean complex impedance (or any portion thereof, e.g.,the real portion, the imaginary portion) of an electrode circuit,including the plasma created and maintained in operational relationshipto an active electrode of a wand, fluid between the active and returnelectrode, and the electrode-fluid interface.

A proximity that is in “operational relationship with tissue” shall meana proximity wherein the tissue interacting with a plasma affects theimpedance presented by the plasma to electrical current flow through theplasma.

A fluid conduit said to be “within” an elongate shaft shall include notonly a separate fluid conduit that physically resides within an internalvolume of the elongate shaft, but also situations where the internalvolume of the elongate shaft is itself the fluid conduit.

Where a range of values is provided, it is understood that everyintervening value, between the upper and lower limit of that range andany other stated or intervening value in that stated range isencompassed within the invention. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein.

All existing subject matter mentioned herein (e.g., publications,patents, patent applications and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such material by virtue of prior invention.

DETAILED DESCRIPTION

Before the various embodiments are described in detail, it is to beunderstood that this invention is not limited to particular variationsset forth herein as various changes or modifications may be made, andequivalents may be substituted, without departing from the spirit andscope of the invention. As will be apparent to those of skill in the artupon reading this disclosure, each of the individual embodimentsdescribed and illustrated herein has discrete components and featureswhich may be readily separated from or combined with the features of anyof the other several embodiments without departing from the scope orspirit of the present invention. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,process, process act(s) or step(s) to the objective(s), spirit or scopeof the present invention. All such modifications are intended to bewithin the scope of the claims made herein.

The various embodiments are directed to electrosurgical methods andrelated electrosurgical systems. In particular, example embodiments aredirected to an electrosurgical system that has the ability to monitorthe active electrode of an electrosurgical wand, to determine inreal-time (during use of the electrosurgical wand) that the activeelectrode is approaching or exceeded the active electrode's useful lifeand/or to detect a clog condition, and to provide an indication orwarning. The various embodiments are discussed first in the context ofuseful life detection, but as will be discussed more below the sametechniques can be used for clog detection. Moreover, the variousembodiments of determining the state of the useful life of the activeelectrode may be implemented with electrosurgical controllers that havemultiple modes of ablation with varying amounts of applied energy. Thespecification first turns to an illustrative system to orient thereader.

FIG. 1 illustrates an electrosurgical system 100 in accordance with atleast some embodiments. In particular, the electrosurgical system 100comprises an electrosurgical wand 102 (hereinafter “wand 102”) coupledto an electrosurgical controller 104 (hereinafter “controller 104”). Thewand 102 comprises an elongate shaft 106 that defines distal end 108.The elongate shaft 106 further defines a handle or proximal end 110,where a physician grips the wand 102 during surgical procedures. Thewand 102 further comprises a flexible multi-conductor cable 112 housingone or more electrical leads (not specifically shown in FIG. 1), and theflexible multi-conductor cable 112 terminates in a wand connector 114.As shown in FIG. 1, the wand 102 couples to the controller 104, such asby a controller connector 120 on an outer surface of the enclosure 122(in the illustrative case of FIG. 1, the front surface).

Though not visible in the view of FIG. 1, in some embodiments the wand102 has one or more internal fluid conduits coupled to the externallyaccessible tubular members. As illustrated, the wand 102 has a flexibletubular member 116, used to provide aspiration at the distal end 108 ofthe wand. In accordance with example systems, the tubular member 116couples to a peristaltic pump 118, which peristaltic pump 118 isillustratively shown as an integral component with the controller 104(i.e., residing at least partially within the enclosure 122 of thecontroller 104). In other embodiments, an enclosure for the peristalticpump 118 may be separate from the enclosure 122 for the controller 104(as shown by dashed lines in the figure)(e.g., bolted to the outside ofthe enclosure), but in any event the peristaltic pump may be operativelycoupled to the controller 104.

The example peristaltic pump 118 comprises a rotor portion 124(hereafter just “rotor 124”) as well as a stator portion 126 (hereafterjust “stator 126”). The flexible tubular member 116 couples within theperistaltic pump 118 between the rotor 124 and the stator 126, andmovement of the rotor 124 against the flexible tubular member 116 causesfluid movement toward the discharge 128. While the illustrativeperistaltic pump 118 is shown with a two-roller rotor 124, varying typesof peristaltic pumps 118 may be used (e.g., a five-roller peristalticpump). In other example systems, the tubing 116 may couple to any sourceof vacuum, such as a vacuum source available in most hospital and/orsurgical centers.

Still referring to FIG. 1, a display device or interface device 130 isvisible through the enclosure 122 of the controller 104. The exampleinterface device 130 may be used select operational modes of thecontroller 104 (either directly on the interface device 130 or by way ofrelated buttons 132), and the interface device 130 may also be thelocation where information is provided to the surgeon. For example, theinterface device 130 may display an indication that the active electrodeof the wand 102 is approaching, has reached, or has exceeded the usefullife of the active electrode. Various aspects of determining the stateof the useful life of the electrode are discussed in more detail below.

In some embodiments the electrosurgical system 100 also comprises a footpedal assembly 134. The foot pedal assembly 134 may comprise one or morepedal devices 136 and 138, a flexible multi-conductor cable 140 and apedal connector 142. While only two pedal devices 136 and 138 are shown,one or more pedal devices may be implemented. The enclosure 122 of thecontroller 104 may comprise a corresponding connector 144 that couplesto the pedal connector 142. A physician may use the foot pedal assembly134 to control various aspects of the controller 104, such as the modeof ablation. For example, pedal device 136 may be used for on-offcontrol of the application of radio frequency (RF) energy to the wand102, and more specifically for control of energy in a mode of ablation.Further, pedal device 138 may be used to control and/or set the mode ofablation of the electrosurgical system. For example, actuation of pedaldevice 138 may switch between energy levels created by the controller104 and aspiration volume created by the peristaltic pump 118. Incertain embodiments, control of the various operational or performanceaspects of controller 104 may be activated by selectively depressingfinger buttons located on handle 110 of wand 102 (the finger buttons notspecifically shown so as not to unduly complicate the figure).

The electrosurgical system 100 of the various embodiments may have avariety of modes of ablation which employ Coblation® technology. Inparticular, the assignee of the present disclosure is the owner ofCoblation® technology. Coblation® technology involves the application ofa radio frequency (RF) signal between one or more active electrodes andone or more return electrodes of the wand 102 to develop high electricfield intensities in the vicinity of the target tissue. The electricfield intensities may be sufficient to vaporize an electricallyconductive fluid over at least a portion of the one or more activeelectrodes in the region between the one or more active electrodes andthe target tissue. The electrically conductive fluid may be inherentlypresent in the body, such as blood, or in some cases extracelluar orintracellular fluid. In other embodiments, the electrically conductivefluid may be a liquid or gas, such as isotonic saline. In someembodiments, such as surgical procedures involving a knee or shoulder,the electrically conductive fluid is delivered in the vicinity of theactive electrode and/or to the target site by a delivery system separateand apart from the system 100.

When the electrically conductive fluid is heated to the point that theatoms of the fluid vaporize faster than the atoms recondense, a gas isformed. When sufficient energy is applied to the gas, the atoms collidewith each other causing a release of electrons in the process, and anionized gas or plasma is formed (the so-called “fourth state ofmatter”). Stated otherwise, plasmas may be formed by heating a gas andionizing the gas by driving an electric current through the gas, or bydirecting electromagnetic waves into the gas. The methods of plasmaformation give energy to free electrons in the plasma directly,electron-atom collisions liberate more electrons, and the processcascades until the desired degree of ionization is achieved. A morecomplete description of plasma can be found in Plasma Physics, by R. J.Goldston and P. N. Rutherford of the Plasma Physics Laboratory ofPrinceton University (1995), the complete disclosure of which isincorporated herein by reference.

As the density of the plasma becomes sufficiently low (i.e., less thanapproximately 1020 atoms/cm³ for aqueous solutions), the electron meanfree path increases such that subsequently injected electrons causeimpact ionization within the plasma. When the ionic particles in theplasma layer have sufficient energy (e.g., 3.5 electron-Volt (eV) to 5eV), collisions of the ionic particles with molecules that make up thetarget tissue break molecular bonds of the target tissue, dissociatingmolecules into free radicals which then combine into gaseous or liquidspecies. By means of the molecular dissociation (as opposed to thermalevaporation or carbonization), the target tissue is volumetricallyremoved through molecular dissociation of larger organic molecules intosmaller molecules and/or atoms, such as hydrogen, oxygen, oxides ofcarbon, hydrocarbons and nitrogen compounds. The molecular dissociationcompletely removes the tissue structure, as opposed to dehydrating thetissue material by the removal of liquid within the cells of the tissueand extracellular fluids, as occurs in related art electrosurgicaldesiccation and vaporization. A more detailed description of themolecular dissociation can be found in commonly assigned U.S. Pat. No.5,697,882 the complete disclosure of which is incorporated herein byreference.

The energy density produced by electrosurgical system 100 at the distalend 108 of the wand 102 may be varied by adjusting a variety of factors,such as: the number of active electrodes; electrode size and spacing;electrode surface area; asperities and/or sharp edges on the electrodesurfaces; electrode materials; applied voltage; current limiting of oneor more electrodes (e.g., by placing an inductor in series with anelectrode); electrical conductivity of the fluid in contact with theelectrodes; density of the conductive fluid; the temperature of theconductive fluid; and other factors. Accordingly, these factors can bemanipulated to control the energy level of the excited electrons. Sincedifferent tissue structures have different molecular bonds, theelectrosurgical system 100 may be configured to produce energysufficient to break the molecular bonds of certain tissue butinsufficient to break the molecular bonds of other tissue. For example,fatty tissue (e.g., adipose) has double bonds that require an energylevel higher than 4 eV to 5 eV (i.e., on the order of about 8 eV) tobreak. Accordingly, the Coblation® technology in some modes of ablationdoes not ablate such fatty tissue; however, the Coblation® technology atthe lower energy levels may be used to effectively ablate cells torelease the inner fat content in a liquid form. Other modes of ablationmay have increased energy such that the double bonds can also be brokenin a similar fashion as the single bonds (e.g., increasing voltage orchanging the electrode configuration to increase the current density atthe electrodes). A more complete description of the various phenomenacan be found in commonly assigned U.S. Pat. Nos. 6,355,032, 6,149,120and 6,296,136, the complete disclosures of which are incorporated hereinby reference.

FIG. 2 shows an elevation view of wand 102 in accordance with examplesystems. In particular, wand 102 comprises elongate shaft 106 which maybe flexible or rigid, a handle 110 coupled to the proximal end of theelongate shaft 106, and an electrode support member 200 coupled to thedistal end of elongate shaft 106. Also visible in FIG. 2 is the flexibletubular member 116 extending from the wand 102 and the multi-conductorcable 112. The wand 102 comprises an active electrode 202 disposed onthe distal end 108 of the elongate shaft 106. Active electrode 202 maybe coupled to an active or passive control network within controller 104(FIG. 1) by means of one or more insulated electrical connectors (notshown) in the multi-conductor cable 112. The active electrode 202 iselectrically isolated from a common or return electrode 204 which isdisposed on the shaft proximal of the active electrode 202, in someexample systems within 1 millimeter (mm) to 25 mm of the distal tip.Proximally from the distal tip, the return electrode 204 located alongthe elongate shaft 106 of the wand 102. The support member 200 ispositioned distal to the return electrode 204 and may be composed of anelectrically insulating material such as epoxy, plastic, ceramic,silicone, glass or the like. Support member 200 extends from the distalend 108 of elongate shaft 106 (usually about 1 to 20 mm) and providessupport for active electrode 202.

FIG. 3 shows a cross-sectional elevation view of the wand 102 inaccordance with example embodiments. In particular, wand 102 comprises asuction lumen 300 defined within the elongate shaft 106. In the examplewand 102 of FIG. 3, the inside diameter of the elongate shaft 106defines the suction lumen 300, but in other cases a separate tubingwithin the elongate shaft 106 may define the suction lumen 300. Thesuction lumen 300 may be used for aspirating excess fluids, bubbles,tissue fragments, and/or products of ablation from the target sitethrough one or more apertures in or around the active electrode 202.Suction lumen 300 extends into the handle 110 and fluidly couples to theflexible tubular member 116 for coupling to the peristaltic pump 118(FIG. 1) or other source of aspiration suction. Handle 110 also definesan inner cavity 302 within which electrical conductors 210 may reside,where the electrical conductors 210 may extend into the multi-conductorcable 112 and ultimately couple to the controller 104 (FIG. 1). Theelectrical conductors 210 likewise extend through the elongate shaft andcouple, one each, to the return electrode 204 and the active electrode202, but the electrical conductors 210 are not shown to reside withinthe elongate shaft 106 so as not to unduly complicate the figure.

In some systems, the wand 102 may further comprise a temperaturemeasurement device positioned to measure a temperature associated withthe fluid drawn in from the vicinity of the active electrode. In theexample system of FIG. 3, temperature measurement device 304 is inoperational relationship to the flexible tubular member 116. Asillustrated in FIG. 3, the temperature measurement device resides withinthe inner cavity 302 defined by the handle 110, but the temperaturemeasurement device may be placed at any suitable location. Asillustrated, the temperature measurement device 304 abuts an outersurface of the tubular member 116 such that as fluids travel within thetubular member 116 past the location of the temperature measurementdevice 304, localized temperature changes can be read. The temperaturemeasurement device 304 may take any suitable form, such as a resistivethermal device (RTD), a thermistor, an optical temperature probe, or athermocouple. Temperature measured by the temperature measurement device304 may be useful in a variety of operational circumstances, such aspart of the determination of state of the useful life of the activeelectrode 202 and/or clog detection, both of which are discussed morebelow.

Still referring to FIG. 3, in example systems the wand 102 may haveprocessor 306 disposed within inner cavity 302. The processor 302 may bea microcontroller from any of a variety of available sources, such asone of the many microcontrollers available from FreescaleSemiconductors, Inc. of Austin, Tex. The processor 302 may have onboardnon-volatile memory 308 within which various programs and data may bestored. In example systems, the non-volatile memory 308 may store aprogram that, when executed by the processor, causes the processor 306to periodically read temperature measurement device 304 (electricallycoupled to the processor 306) and then digitally send the temperaturevalues to the controller 104 by way of conductors 310. The processor 306may be powered from the controller 104 through the multi-conductor cable112, such as by conductors 312. The non-volatile memory 308 may alsostore parameters associated with the determinations regarding usefullife of the active electrode 202, which parameters are discussed ingreater detail below.

In yet still further cases, the temperature measurement device may beassociated with the suction lumen 300. For example, the assignee of thecurrent specification has a technology directed to a temperaturemeasurement device on the elongate shaft 106 proximal of the returnelectrode 204. Such a temperature measurement device may be primarilyresponsive to the temperature surrounding the elongate shaft 106, butsuch location for the temperature measurement device would also make thedevice secondarily responsive to temperature of fluid drawn into thesuction lumen 300 from the vicinity of the active electrode. Thus,temperature measurements closer to the active electrode may also be usedalone or in combination with the temperature measurement device 304 forthe temperature aspects of the various embodiments. Reference is alsomade to commonly assigned U.S. Pat. No. 8,696,659, entitled“ELECTROSURGICAL SYSTEM AND METHOD HAVING ENHANCED TEMPERATUREMEASUREMENT”, the complete disclosure of which is incorporated herein byreference as if reproduced in full below.

FIG. 4 shows an elevation view of an example active electrode (on theleft), as well as a perspective view of the distal end of wand 102 (onthe right), in accordance with example systems. In particular, activeelectrode 202 may be an active screen electrode 400 as shown in FIG. 4.Screen electrode 400 may comprise a conductive material, such astungsten, titanium, molybdenum, platinum, or the like. Prior to thefirst use, screen electrode 400 may have a diameter in the range ofabout 0.5 to 8 mm, in some cases about 1 to 4 mm, and a thickness ofabout 0.05 to about 2.5 mm, in some cases about 0.1 to 1 mm. Screenelectrode 400 may comprise a plurality of apertures 402 configured torest over an aperture or distal opening 404 of the suction lumen.Apertures 402 enable the passage of aspirated excess fluids, bubbles,and gases from the ablation site, and the apertures 402 are large enoughto enable ablated tissue fragments to pass through into suction lumen300 (FIG. 3). As shown, screen electrode 400 has an irregular shapewhich increases the edge to surface-area ratio of the screen electrode400. A large edge to surface-area ratio increases the ability of screenelectrode 400 to initiate and maintain a plasma layer in conductivefluid because the edges generate higher current densities, which a largesurface area electrode tends to dissipate power into the conductivemedia.

In the representative embodiment shown in FIG. 4, screen electrode 400comprises a body 406 that rests over insulative support member 200 andthe distal opening 404 to suction lumen 300. Screen electrode 400further comprises tabs 408, in the example screen electrode 400 of FIG.4, five tabs 408 are shown. The tabs 408 may rest on, be secured to,and/or be embedded in insulative support member 200. In certainembodiments, electrical connectors extend through insulative supportmember 200 and are coupled (i.e., via adhesive, braze, weld, or thelike) to one or more of tabs 408 in order to secure screen electrode 400to the insulative support member 200 and to electrically couple screenelectrode 400 to controller 104 (FIG. 1). In example systems, screenelectrode 400 forms a substantially planar tissue treatment surface forsmooth resection, ablation, and sculpting of the meniscus, cartilage,and other tissues. In reshaping cartilage and meniscus, the physicianoften desires to smooth the irregular and ragged surface of the tissue,leaving behind a substantially smooth surface. For these applications, asubstantially planar screen electrode treatment surface provides thedesired effect. The specification now turns to a more detaileddescription of the controller 104.

FIG. 5 shows an electrical block diagram of controller 104 in accordancewith example systems. In particular, the controller 104 comprises aprocessor 500. The processor 500 may be a microcontroller, and thereforethe microcontroller may be integral with read-only memory (ROM) 502,random access memory (RAM) 504, digital-to-analog converter (D/A) 506,analog-to-digital converter (A/D) 514, digital outputs (D/O) 508, anddigital inputs (D/I) 510. The processor 500 may further provide one ormore externally available peripheral busses, such as a serial bus (e.g.,I²C), parallel bus, or other bus and corresponding communication mode.The processor 500 may further be integral with communication logic 512to enable the processor 500 to communicate with external devices, aswell as internal devices, such as display device 130. Although in someembodiments the processor 500 may be implemented in the form of amicrocontroller, in other embodiments the processor 500 may beimplemented as a standalone central processing unit in combination withindividual RAM, ROM, communication, A/D, D/A, D/O, and D/I devices, aswell as communication hardware for communication to peripheralcomponents.

ROM 502 stores instructions executable by the processor 500. Inparticular, the ROM 502 may comprise a software program that, whenexecuted, causes the controller to determine the presence or absence ofvarious wand conditions, such as the active electrode of the wand 102approaching, reaching, or exceeding the useful life of the activeelectrode. Similarly, the program, when executed, causes the controllerto determine the presence or absence of a clog associated with the wand102. The RAM 504 may be the working memory for the processor 500, wheredata may be temporarily stored and from which instructions may beexecuted. Processor 500 couples to other devices within the controller104 by way of the digital-to-analog converter 506 (e.g., in someembodiment the RF voltage generator 516), digital outputs 508 (e.g., insome embodiment the RF voltage generator 516), digital inputs 510 (e.g.,interface devices such as push button switches 132 or foot pedalassembly 134 (FIG. 1)), and communication device 512 (e.g., displaydevice 130).

Voltage generator 516 generates an alternating current (AC) voltagesignal that is coupled to active electrode 202 of the wand 102 (FIG. 3).In some embodiments, the voltage generator defines an active terminal518 which couples to electrical pin 520 in the controller connector 120,electrical pin 522 in the wand connector 114, and ultimately to theactive electrode 202 (FIG. 3). Likewise, the voltage generator defines areturn terminal 524 which couples to electrical pin 526 in thecontroller connector 120, electrical pin 528 in the wand connector 114,and ultimately to the return electrode 204 (also FIG. 3). Additionalactive terminals and/or return terminals may be used. The activeterminal 518 is the terminal upon which the voltages and electricalcurrents are induced by the voltage generator 516, and the returnterminal 524 provides a return path for electrical currents. It would bepossible for the return terminal 524 to provide a common or ground beingthe same as the common or ground within the balance of the controller104 (e.g., the common 530 used on push-buttons 132), but in otherembodiments the voltage generator 516 may be electrically “floated” fromthe balance of the controller 104, and thus the return terminal 524,when measured with respect to the common or earth ground (e.g., common530) may show a voltage; however, an electrically floated voltagegenerator 516 and thus the potential for voltage readings on the returnterminals 524 relative to earth ground does not negate the returnterminal status of the terminal 524 relative to the active terminal 518.

The AC voltage signal generated and applied between the active terminal518 and return terminal 524 by the voltage generator 516 is RF energythat, in some embodiments, has a frequency of between about 5 kilo-Hertz(kHz) and 20 Mega-Hertz (MHz), in some cases being between about 30 kHzand 2.5 MHz, in other cases being between about 50 kHz and 500 kHz,often less than 350 kHz, and often between about 100 kHz and 200 kHz. Insome applications, a frequency of about 100 kHz is useful because targettissue impedance is greater at 100 kHz.

The RMS (root mean square) voltage generated by the voltage generator516 may be in the range from about 5 Volts (V) to 1800 V, in some casesin the range from about 10 V to 500 V, often between about 10 V to 400 Vdepending on the mode of ablation and active electrode size. Thepeak-to-peak voltage generated by the voltage generator 516 for ablationin some embodiments is a square waveform with a peak-to-peak voltage inthe range of 10 V to 2000 V, in some cases in the range of 100 V to 1800V, in other cases in the range of about 28 V to 1200 V, and often in therange of about 100 V to 320V.

The voltage and current generated by the voltage generator 516 may bedelivered in a series of voltage pulses or AC voltage with asufficiently high frequency (e.g., on the order of 5 kHz to 20 MHz) suchthat the voltage is effectively applied continuously (as compared with,e.g., lasers claiming small depths of necrosis, which are pulsed about10 Hz to 20 Hz). In addition, the duty cycle (i.e., cumulative time inany one-second interval that energy is applied) of a square wave voltageproduced by the voltage generator 516 is on the order of about 50% forsome embodiments as compared with pulsed lasers which may have a dutycycle of about 0.0001%. Although square waves are generated and providedin some embodiments, the AC voltage signal is modifiable to include suchfeatures as voltage spikes in the leading or trailing edges of eachhalf-cycle, or the AC voltage signal is modifiable to take particularshapes (e.g., sinusoidal, triangular).

The voltage generator 516 delivers average energy levels ranging fromseveral milliwatts to hundreds of watts per electrode, depending on themode of ablation and state of the plasma proximate to the activeelectrode. In example systems, the voltage generator 516 in combinationwith the processor 500 are configured to initially set the energy outputof the voltage generator 516 (e.g., by controlling output voltage) basedon the mode of ablation selected by the surgeon, and in some cases thesetpoint within the particular mode of ablation. Moreover, while in aselected mode of ablation and setpoint within the mode of ablation, theprocessor 500 and/or voltage generator 516 may make control changes tocompensate for changes caused by use of the wand. A description ofvarious voltage generators 516 can be found in commonly assigned U.S.Pat. Nos. 6,142,992 and 6,235,020, the complete disclosure of bothpatents are incorporated herein by reference for all purposes. Referenceis also made to commonly assigned U.S. Pat. No. 8,257,350, entitled“METHOD AND SYSTEM OF AN ELECTROSURGICAL CONTROLLER WITH WAVE-SHAPING”,the complete disclosure of which is incorporated herein by reference asif reproduced in full below.

In example systems the voltage generator 516 (along with the peristalticpump 118) may be controlled by the processor 500 by way ofdigital-to-analog converter 506. For example, the processor 500 maycontrol the output voltages by providing one or more variable voltagesto the voltage generator 516, where the voltages provided by thedigital-to-analog converter 506 are proportional to the voltages to begenerated by the voltage generator 516. In other embodiments, theprocessor 500 may communicate with the voltage generator by way of oneor more digital output signals from the digital output converter 508, orby way of packet-based communications using the communication device 512(the communication-based embodiments not specifically shown so as not tounduly complicate FIG. 5).

Before proceeding, it is noted that the various embodiments of detectingthe state of the useful life of the active electrode, and/or clogdetection, may be implemented on systems having a single mode ofablation. Stated otherwise, determining the useful life of the activeelectrode and/or presence of a clog is not limited to systems havingmultiple modes of ablation.

During use of the controller 104, the electrode circuit (including theplasma created and maintained in operational relationship to the activeelectrode of a wand, the fluid between the active and return electrode,and the electrode-fluid interface) has or presents a certain amount ofimpedance to the flow of energy from the active electrode toward areturn electrode. The impedance presented by the electrode circuit maybe dependent on many factors, including but not limited to the thicknessand volume of the plasma itself, the surface area of the activeelectrode, the surface area of the active electrode not covered by avapor layer and directly in contact with the conductive fluid, and thevolume flow of fluid and/or gasses away from the location of the plasma.In example systems, voltage generator 516 is a “constant voltagesource”, meaning that the voltage generator 516 provides the voltagerequested by the processor 500 (at the frequency and duty cycle) largelyindependent of the impedance presented by the electrode circuit. In suchsystems, the controller 104 may comprise a mechanism to sense theelectrical current provided to the active electrode. In the illustrativecase of FIG. 3, sensing electrical current provided to the activeelectrode may be by way of a current sense transformer 532. Inparticular, current sense transformer 532 may have a conductor of theactive terminal 518 threaded through the transformer such that theactive terminal 518 becomes a single turn primary. Current flow in thesingle turn primary induces corresponding voltages and/or currents inthe secondary. Thus, the illustrative current sense transformer 532 iscoupled to the digital-to-analog converter 514 (as shown by the bubbleA). In some cases, the current sense transformer may couple directly tothe analog-to-digital converter 514, and in other cases additionalcircuitry may be imposed between the current sense transformer 532 andthe digital-to-analog converter 514, such as amplification circuits andprotection circuits. For example, in one example system the currentsense transformer 532 is coupled to an integrated circuit device thattakes the indication of current from the current sense transformer 532,calculates a RMS current value, and provides the RMS current values tothe processor 500 through any suitable communication system (e.g., as ananalog value applied the ND 514, as a digital value applied to themultiple inputs of the D/I 510, as a packet message through thecommunication port 512). The current sense transformer is merelyillustrative of any suitable mechanism to sense the electrical currentsupplied to the active electrode, and other systems are possible. Forexample, a small resistor (e.g., 1 Ohm, 0.1 Ohm) may be placed in serieswith the active terminal 518, and the voltage drop induced across theresistor used as an indication of the electrical current.

Given that the voltage generator 516 is electrically floated, themechanism to sense current is not limited to the just the activeterminal 518. Thus, in yet still further embodiments, the mechanism tosense current may be implemented with respect to the return terminal524. For example, illustrative current sense transformer 532 may beimplemented on a conductor associated with the return terminal 524.

While the example voltage generator of FIG. 4 is a “constant voltagesource”, and thus electrical current may change based on the impedancepresented by the electrode circuit, other types of generators may beimplemented in connection with determining useful life of the activeelectrode and/or clog detection. For example, the generator may be a“constant current source”, in which case the voltage applied to theactive terminal may change depending on the impedance. In the “constantcurrent source” situation the electrical current may be known based onthe setpoint, and thus the voltage as measured between the activeterminal and the return terminal may change depending on the impedance.Regardless of the type of generator, knowing the “constant” electricalparameter and measuring a changing electrical parameter enables thecontroller 104 to calculate power supplied to the active electrode 202of the wand 102. However, power is merely the product of electricalcurrent and applied voltage, and thus for a “constant voltage source”the electrical current alone is directly indicative of power provided.Likewise, for a “constant current source” the applied voltage alone isdirectly indicative of power provided. It follows that the controllerneed not necessarily calculate power to monitor electrical energysupplied to the active electrode.

Even in the case of a constant voltage source, the controller 104 maynevertheless measure voltage. Thus, in some cases the active terminal518 may be electrically coupled to the digital-to-analog converter 514(as shown by bubble B). However, additional circuitry may be imposedbetween the active terminal 518 and the digital-to-analog converter 514,for example various step-down transformers, protection circuits, andcircuits to account for the electrically floated nature of the voltagegenerator 516. Such additional circuitry is not shown so as not tounduly complicate the figure. In yet still other cases, voltage sensecircuitry may measure the voltage, and the measured voltage values maybe provided other than by analog signal, such as by way of packet-basedcommunications over the communication port 512 (not shown so as not tounduly complicate the drawing).

Still referring to FIG. 5 (and also FIG. 1), controller 104 inaccordance with example systems further comprises peristaltic pump 118.The peristaltic pump comprises rotor 124 mechanically coupled to a shaftof the electric motor 534. In some cases, and as illustrated, the rotorof the electric motor may couple directly to the rotor 124, but in othercases various gears, pulleys, and/or belts may reside between theelectric motor 534 and the rotor 124. The electric motor 534 may takeany suitable form, such as an AC motor, a DC motor, and/or astepper-motor. To control speed of the shaft of the electric motor 534,and thus to control speed of the rotor 124 (and the volume flow rate atthe wand), the electric motor 534 may be coupled to a motor speedcontrol circuit 536. In the illustrative case of an AC motor, the motorspeed control circuit 536 may control the voltage and frequency appliedto the electric motor 534. In the case of a DC motor, the motor speedcontrol circuit 536 may control the DC voltage applied to the electricmotor 534. In the case of a stepper-motor, the motor speed controlcircuit 536 may control the current flowing to the poles of the motor,but the stepper-motor may have a sufficient number of poles, or iscontrolled in such a way, that the rotor 124 moves smoothly. Statedotherwise, the rotor 124 moves smoothly due to the high number of stepsper turn.

The processor 500 couples to the motor speed control circuit 536, suchas by way of the digital-to-analog converter 506 (as shown by bubble C).The processor 500 may be coupled in other ways as well, such aspacket-based communication over the communication port 512. Thus, theprocessor 500, running a program, may read electrical current suppliedon the active terminal 518, may read voltage supplied on the activeterminal 518, and responsive thereto may make speed control changes (andthus volume flow rate changes) by sending speed commands to the motorspeed control circuit 536. The motor speed control circuit 536, in turn,implements the speed control changes. Speed control changes may comprisechanges in speed of the rotor 124 when desired, stopping the rotor 124when desired, and in some modes of ablation temporarily reversing therotor 124.

State of the Useful Life of the Active Electrode

The specification now turns to example embodiments of detecting when theactive electrode of the wand 102 is approaching, has reached, or hasexceeded the useful life of the active electrode 202. When a wand 102 isnew, the active electrode 202 has a certain size, a certain exposedsurface area (e.g., that portion not abutting the spacer 200), andvarious edges or asperities. However, plasma created proximate theactive electrode 202 molecularly dissociates tissue proximate theplasma, and the plasma also removes (i.e., etches) material of theactive electrode 202 itself. As the etching takes place, the exposedsurface area of the active electrode 202 is reduced, and the sharp edgesare smoothed.

After a certain amount of use, while metallic material of the activeelectrode 202 may still be present on the distal tip of the wand, thesize of the plasma created proximate the active electrode 202 may bereduced (because of the smaller exposed surface area) to the point thatthe therapeutic benefit is no longer achievable, or the reducedtherapeutic benefit is outweighed by other factors (e.g., damage causedby extending the time of the procedure, non-ablative contact with tissuewithin the joint that causes bruising or further injury). Similarly, foran active electrode 202 such as discussed above where the aspiration ofthe ablated tissue and other fluids is through the active electrode 202itself, after a certain amount of use the reduction in the metallicmaterial present on the active electrode 202 may increase the size ofthe aperture 402 through the active electrode 202. Thus, aspiration flowmay increase (compared to a “new” wand 102) to the point that thetherapeutic benefit is no longer achievable, or the reduced therapeuticbenefit is outweighed by other factors. If follows that, in discussinguseful life of an active electrode, it is to be understood that theactive electrode 202 may still be physically present and perhaps usable,at least in a limited sense, at the point in time that the “useful life”has been met or exceeded.

Even with a new active electrode, during ablative procedures theimpedance presented by the electrode circuit may vary significantly. Forexample, impedance presented during periods of time when the activeelectrode 202 is close to and is ablating tissue is relatively high.Impedance may be relatively low when the wand is active but in salinewith high flow. Different impedance may be presented by the electrodecircuit based on different tissue types being ablated. Moreover, duringuse the plasma periodically is extinguished and re-ignited, causingimpedance changes.

As the exposed surface area of the active electrode 202 is reduced, theimpedance presented by the electrode circuit is increased. Anothercharacteristic of an active electrode when exposed surface area isreduced is that creation and forming the vapor layer around the activeelectrode 202 is easier and thus creation of and maintaining plasma bythe controller 104 is easier. It follows that variation in impedancepresented by the electrode circuit is reduced as the exposed surfacearea of the active electrode is reduced.

In accordance with example embodiments, the controller 104 may make adetermination as to the state of the useful life of the active electrodebased on an electrical parameter associated with the plasma. Moreparticularly, in example systems the controller 104 may maintain plasmaproximate the active electrode 202, and during periods of time whenplasma is present the controller 104 monitors the electrical parameterassociated with the plasma. For example, in cases where the generator516 is a constant voltage source generator, the controller may monitorelectrical current supplied on the active terminal 518 (e.g., monitor byway of current sense transformer 532). In cases where the generator is aconstant current source generator, the controller may monitor voltagesupplied across the active terminal 518 and return terminal 524. In somecases the monitored electrical parameter alone is sufficiently relatedto impedance that an actual value of impedance need not be calculated,but having the controller 104 calculate a value of impedance is alsopossible. In other cases, power delivered to the electrode circuit(which is also related to impedance) may be calculated.

Regardless of the electrical parameter monitored or calculated, inexample systems the controller 104 further determines, based on theelectrical parameter, the presence of a wand condition of theelectrosurgical wand 102. The wand condition may be that the exposedsurface area of the active electrode is less than a predeterminedthreshold surface area (e.g., the wand has exceeded its useful life), orthat the surface area of the active electrode is approaching thepredetermined threshold surface area (e.g., the wand is approaching theend of its useful life).

In accordance with example systems, the determination regarding state ofthe useful life of the active electrode may be based on variation of theelectrical parameter over a predetermined period of use. That is, over apredetermined period of use (e.g., the immediately previous 5 to 15seconds of use), the controller 104 may calculate a value indicative ofvariation of the monitored electrical parameter (hereafter just“variation metric”), and make the determination based on the variationmetric. For example, if the variation metric gets smaller as thevariation in impedance presented by the electrode circuit is reduced,then the controller may determine that the wand condition is presentwhen the variation metric falls below a predetermined value. It is alsopossible to calculate a variation metric that is inversely proportionalto variation of the electrical parameter (e.g., increases as thevariation in impedance presented by the electrode circuit is reduced),and in such cases the controller may determine that the wand conditionis present when the variation metric meets or exceeds a predeterminedvalue.

In some example systems, the variation metric alone is sufficient todetermine when the active electrode is approaching, has met, or hasexceeded its useful life. However, variations in impedance presented inthe electrode circuit during use may mimic a worn electrode when theelectrode still has useful life, or may mask the fact that the activeelectrode is worn. In yet still further example systems then, thedetermination as to the state of the active electrode may also be basedon or confirmed by other measured or monitored parameters.

Referring briefly to FIGS. 3 and 4, in the example system discussed inthis specification aspiration of the ablated tissue and other fluids isthrough an aspiration aperture 402 in the active electrode and acorresponding distal opening 404 in the wand 102. The ablated tissue andother fluids move through the suction lumen 300 and then through thetubular member 116 past the temperature measurement device 304.Controller 104 may thus read the temperature (or a value indicative oftemperature) of the aspirated fluids by way of the temperaturemeasurement device 304. When a wand 102 is new and the active electrodehas its largest exposed surface area, the amount of energy that can beapplied to the plasma and surrounding tissue is high, but as the exposedsurface area is reduced the amount of energy that can be applied isreduced. It follows that the temperature of the fluids drawn into thesuction lumen 300 and through the tubular member 116 is reduced as theexposed surface area of the active electrode is reduced.

In further example systems, the determination as to whether the activeelectrode is approaching, has reached, or has exceeded its useful lifemay be further based on the temperature measured by the temperaturemeasurement device 304 during the predetermined period of use. Inparticular, during the predetermined period of use (e.g., theimmediately previous 5 to 15 seconds of use) the controller 104calculates the variation metric, reads the temperature of the aspiratedfluids, and makes the determination as to the state of the useful lifeof the active electrode based on the variation metric and thetemperature. For example, the controller 104 may determine that the wandcondition is present when the variation metric falls below apredetermined value and one of the following temperature conditions ispresent: the temperature is below a predetermined threshold temperature;the temperature is above the predetermined threshold temperature buttrending toward the predetermined threshold temperature; the temperatureis trending downward (regardless of initial temperature); or the rate ofchange of the temperature (i.e., the slope) meets or exceeds apredetermined rate.

If the temperature is below the predetermined threshold temperature,such may indicate that the exposed surface area of the active electrodehas been reduced and therefore the amount of energy that can be appliedby the controller 104 (and the temperature of the surrounding fluid) issimilarly reduced. Thus, the temperature being below the predeterminedthreshold temperature may be indicative of the active electrode havingexceeded its useful life. As for the second temperature condition, onthe same physical considerations as the first temperature condition, thetemperature being above the predetermined threshold temperature isinitially indicative of an active electrode with remaining useful life,but trending of the temperature downward toward the thresholdtemperature may indicate that the active electrode is approaching theend of its useful life. In yet still other cases, the trend oftemperature may be used with a need to evaluate an initial temperature.For example, for a certain energy input, if the slope is negative, sucha negative slope may be indicative of a worn active electrode. Thespecification now turns to consideration of selecting the predeterminedperiods of use, predetermined values regarding the variation metric,predetermined threshold temperatures, and/or predetermined slopesregarding temperatures.

The various predetermined periods, values, and temperatures may bedifferent for different wands, different uses of the wands, differentenergy levels provided by controllers, different joint and/or roomtemperatures, and different aspiration rates, to name a few. Moreover,some electrosurgical systems, like those discussed in thisspecification, have the ability to operate in varying modes of ablation,and thus a single controller 104 and a single wand 102 may be operatedin several different energy ranges and aspiration rates even within thesame surgical procedure. For example, the controller of thisspecification may implement: a “low mode” which may be used fortreatment, ablation, and removal of portions of cartilage; a “mediummode” which may be used for treatment, ablation, and removal ofmeniscus; a “high mode” which may be used for aggressive treatment,ablation, and removal of tissue; and a “vacuum mode” for removal ofloose, free floating and/or trapped tissue. Each illustrative mode ofablation may be characterized by a range of energies that may be appliedto the active electrode (hereafter just “energy range”) and acorresponding range of aspiration flows.

The various predetermined periods, values, and temperatures will bedifferent for different for different modes of ablation. That is, thepredetermined value of the variation metric that may indicate a wornelectrode in the low mode may be lower than the predetermined value ofthe variation metric that may indicate a worn electrode in the highmode. Similarly, the predetermined threshold temperature that mayindicate a worn electrode in the low mode may be lower than thepredetermined threshold temperature that may indicate a worn electrodein the high mode. Further still, because the variation may be smaller inthe example low mode, the predetermined period of use in the low may belonger than the predetermined period of use in the high mode. It will befurther understood that within the same electrosurgical procedure, asthe surgeon switches between modes of ablation but using the same wand,the various predetermined periods, values, and temperatures may likewisechange. A wand may have a longer useful life if operated exclusively inthe low mode of ablation, but the useful life may get shorter withincreasing use times in the higher modes of ablation.

Determining the various predetermined periods, values, and temperaturesmay be based on laboratory studies that characterize the wands indifferent uses, energy ranges, and aspiration flow rates. Moreover,electrosurgical controllers may have the ability to store dataassociated with an electrosurgical procedure, and based on offlineanalysis engineers may quantify when an active electrode met or exceededits useful life, and then set values for future use accordingly.

In some systems, the various predetermined periods, values, andtemperatures are stored in a non-volatile memory of the controller 104(e.g., the ROM 502). Once the controller 104 identifies the wand (eitherautomatically, or by the user inputting the information using buttons132 and/or display device 130), the appropriate predetermined periods,values, and temperatures are read and applied during use. In othersystems, the various predetermined periods, values, and temperatures arestored on the wand 102. For example, and referring briefly to FIG. 3,the non-volatile memory 308 associated with the processor 306 may storethe various predetermined periods, values, and temperatures (for asingle mode of ablation, or for multiple modes of ablation). Thecontroller 104 may read data from the processor 306 (such as over 310),and then apply the data during the electrosurgical procedure.

Blockage Detection

In researching and developing the various algorithms to determine whenan active electrode has met or exceeded its useful life, the inventorsof the present specification found that the various methods regardingdetermining useful life of the active electrode may also be used todetect clogging of the wand (such as by large pieces of tissue blockingaspiration flow) In particular, when fluid flow through a wand is eitherfully or at least partially blocked, either at the active electrode orwithin the suction tubing, the aspiration flow is reduced or stopscompletely. The reduced or lack of aspiration flow tends to stabilizethe plasma, resulting in a lower variation of impedance presented by theelectrode circuit. Further, because the reduced flow of fluids, thetemperature measured by the temperature measurement device 304 starts tofall. For example, if the temperature measurement device 304 is a RTD,the RTD has a certain thermal mass which will retain the lasttemperature measured, and then show lowering temperatures as the thermalmass of the RTD cools. Thus, the clog situation presents itselfsimilarly to the worn electrode—low variation in impedance and slowlydescending temperatures. In some cases, the controller may not be ableto distinguish between a worn electrode and a clog, and may thusclassify the event as a wand condition that could be either situation.

Flow Diagram

The specification now turns to a description of an exampleimplementation in greater detail. FIG. 6 (comprising FIGS. 6A and 6B)shows a flow diagram of a method which may be implemented on theprocessor 500 of the controller 104. So as not to unduly complicate thefigure and the description, FIG. 6 is based on several underlyingassumptions. First, the flow diagram of FIG. 6 assumes that thegenerator 516 of the controller 104 is applying energy to the activeelectrode 202 of the wand 102 and that the voltage applied is highenough to produce plasma on the active electrode. If the surgeon stopsthe application of energy, the example method implemented by the flowdiagram pauses until such time that the energy is restarted. Second, theflow diagram of FIG. 6 assumes that the energy has been active over aprevious predetermined period of use (and the use over predeterminedperiod of use may be fulfilled by tacking together periods of time whenthe energy is being applied even if separated by periods when the energyhas been turned off). One having ordinary skill in the art, afterunderstanding the example method, could easily modify the programming toaccount for initial use leading up to use over a complete predeterminedperiod of use, and taking into account periods of time when the energyis turned off. Third, the various predetermined periods, values, andtemperatures have already been read by or provided to the controller104, including the various predetermined periods, values, andtemperatures for each mode of ablation if the controller implementsmultiple modes of ablation. Fourth, the variation metric is directlyproportional to variance of the electrical parameter. One havingordinary skill in the art, after understanding the example method, couldeasily modify the programming to account for a variation metric that isinversely proportional to variation of the electrical parameter.

With the assumptions in mind, the method starts (block 600) and proceedsto monitoring an electrical parameter associated with the applied energy(block 602). The monitoring could be measuring electrical currentsupplied to the active electrode, measuring voltage applied across theactive and return electrodes, or calculating further parameters based onthe electrical current or voltage (e.g., impedance, instantaneouspower). In cases where temperature is a component the overalldeterminations, simultaneously with monitoring the electrical parameter,the method may further include reading or measuring temperature of fluidaspirated (block 604) (e.g., reading or measuring a value indicative oftemperature associated with the fluid drawn in the vicinity of theactive electrode).

The illustrative method then proceeds to making a determination as towhether more time remains in the current calculation window (block 606).In particular, the predetermined period of use (e.g., the immediatelyprevious 5 to 15 seconds of use) is conceptually divided into aplurality of calculation windows of time (e.g., four to eightcalculation windows). In one example implementation, each calculationmay be one second in duration, and thus for a predetermined period ofuse of five seconds, five calculation windows may be used. In anotherexample implementation, two second calculation windows may be used, andthus for a predetermined period of use of 14 seconds, seven calculationwindows may be used. Thus, if there is more time needed to complete acalculation window (again block 606), the illustrative method returns(along path 608) to again monitor the electrical parameter (block 602)and measuring the temperature (block 604).

If the time duration of the current calculation window has been met(again block 606), the example method then proceeds to calculating avariation metric over the just-concluded calculation window (block 610).The variation metric can be conceptually thought of as the mathematicalvariance of the measured electrical parameter measurements; however, thecontroller 104 need not necessarily calculate an actual variance value.For example, in order to reduce processing overhead, the variationmetric may be calculated by subtracting measured values betweenconsecutive measurements to obtain difference values, and then summingthe absolute values of the differences values. Other methods tocalculate the variation metric may also be implemented in exampleembodiments, included calculating actual variance if sufficientprocessor cycles are available.

Still referring to FIG. 6A, again in cases where temperature is acomponent the overall determinations, simultaneously with calculatingthe variation metric (block 610), the method may further includecalculating an average temperature over the current calculation window(block 614) assuming many temperature measurements are made in thecalculation window. The method contemplates calculation windows havingonly a single reading or measurement of a value indicative oftemperature, in which case the calculating the average is mooted. Inorder to reduce processor cycles a value proportional to average may becalculated instead of an actual average.

The example method may then proceed to a determination as to whether thevariation metrics are less all than a predetermined value for each ofthe calculation windows (block 616). If the variation metrics are allabove the predetermined value, the active electrode may still havesufficient useful life, and thus the example method retreats to thebeginning (along path 618) to begin anew in the next calculation window.On the other hand, if the variation metrics are all below thepredetermined value, such may indicative that the active electrode 202of the wand 102 is approaching, has reached, or has exceeded its usefullife, or fluid flow through the wand is either fully or at leastpartially blocked. In some example systems the determination regardingthe variation metric alone may be sufficient, and thus the system mayalert the surgeon (block 620) and the example method moves again to thebeginning (along path 622) to begin anew in the next calculation window.

However, in other cases the determination regarding useful life of theactive electrode may be augmented by a temperature component. Thus, ifthe variation metric are below the predetermined threshold (again block616), the example method proceeds to temperature aspects of the overalldetermination. In the first temperature aspect, a determination is madeas to whether the average temperature for each calculation window of thepredetermined measurement period is below a predetermined thresholdtemperature (block 624). If so, the example method proceeds along path626 to alerting the surgeon (again block 620). On the other hand, if theaverage temperature for each calculation window of the predeterminedmeasurement period is above the predetermined threshold temperature(again block 624), the example method moves to a determination as towhether the average temperature of each calculation window, whenconsidered as a group, is trending toward the predetermined thresholdtemperature (block 628). If not, the example method retreats to thebeginning (along path 630) to begin anew in the next calculation window.If so, the method proceeds to alerting the surgeon (again block 620).

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications are possible. As an example, while useful life and/or clogdetection has been described as taking place within an electrosurgicalcontroller, the determinations regarding useful life and/or clogdetection could also be made in a standalone system operationallycoupled to an electrosurgical controller and monitoring the variousparameters. For example, the standalone system could be imposed betweenthe electrosurgical controller and the wand and passively obtain thevarious parameters used to make the useful life and/or clog detection.In other cases, the standalone system may communicatively couple to theelectrosurgical controller and receive data regarding the ablationprocedure, and make the various determinations. It is intended that thefollowing claims be interpreted to embrace all such variations andmodifications.

While preferred embodiments of this disclosure have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the scope or teaching herein. The embodimentsdescribed herein are exemplary only and are not limiting. Because manyvarying and different embodiments may be made within the scope of thepresent inventive concept, including equivalent structures, materials,or methods hereafter thought of, and because many modifications may bemade in the embodiments herein detailed in accordance with thedescriptive requirements of the law, it is to be understood that thedetails herein are to be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. An electrosurgical system comprising: a processor; a memory coupled to the processor; wherein the memory stores a program that, when executed by the processor, causes the processor to: monitor an electrical parameter associated with a voltage generator during periods of time when energy is being delivered to an active electrode of an electrosurgical wand; and determine, based on the electrical parameter, a presence of a wand condition of the electrosurgical wand, the wand condition being at least one selected from the group consisting of: a surface area of the active electrode is less than a predetermined threshold surface area; and that the surface area of the active electrode is approaching the predetermined threshold surface area.
 2. The electrosurgical system of claim 1 further comprising: a voltage generator operatively coupled to the processor, the voltage generator comprising an active terminal; a wand connector configured to couple to a connector of the electrosurgical wand, the wand connector electrically coupled to the active terminal of the voltage generator; wherein the memory stores a program that, when executed by the processor further causes the processor to command the voltage generator to deliver energy to the active electrode of the electrosurgical wand.
 3. The electrosurgical system of claim 1 wherein when the processor determines, the program causes the processor to: calculate a value indicative of variation of the electrical parameter over a predetermined period of use; and determine the presence of the wand condition based on the value indicative of electrical variation.
 4. The electrosurgical system of claim 1 wherein when the processor determines the presence of the wand condition based on the value indicative of variation, the program causes the processor to determine the wand condition as present when the value indicative of variation is below a predetermined value.
 5. The electrosurgical system of claim 3 further comprising; wherein when the processor calculates the value indicative of variation, the program causes the processor to calculate a value indicative of variation for each of a plurality of calculation windows; and wherein when the processor determines the presence of the wand condition, the program causes the processor to determine the wand condition as present when the value indicative of variation for each of the plurality of calculation windows is below a predetermined value.
 6. The electrosurgical system of claim 1 wherein the electrical parameter is selected from the group consisting of: impedance; voltage applied; electrical current applied; and power applied.
 7. The electrosurgical system of claim 1 further comprising: a sensor configured to measure a value indicative of temperature of a fluid drawn from a vicinity of the active electrode, and wherein the program further causes the processor to read a value indicative of temperature over a predetermined period of use; wherein when the processor determines, the program causes the processor to determine based on the electrical parameter and the value indicative of temperature.
 8. The electrosurgical system of claim 7 wherein the sensor is associated with a suction lumen of the electrosurgical wand.
 9. The electrosurgical system of claim 7 wherein when the sensor is associated with a suction lumen, so as to sense a value indicative of temperature of tubing disposed within a handle of the electrosurgical wand.
 10. The electrosurgical system of claim 7: wherein the program causes the processor to calculate a value indicative of variation for each of a plurality of calculation windows, the plurality of calculation windows residing within the predetermined period of use; wherein when the processor determines the presence of the wand condition, the program causes the processor to determining the wand condition as present when the value indicative of variation for each of the plurality of calculation windows is below a predetermined value and the value indicative of temperature is at least one selected from the group consisting of: below a predetermined threshold temperature; above the predetermined threshold temperature with the temperature trending toward the predetermined threshold temperature; trending downward; has or exceeds a predetermined rate of change.
 11. The electrosurgical system of claim 1 further comprising: wherein the program further causes the processor to: calculate a value indicative of variation of the electrical parameter over a predetermined period of use; and read a value indicative of temperature associated with fluid drawn from a vicinity of the active electrode, over the predetermined period of use; wherein when the processor determines the presence of the wand condition, the program causes the processor to determine based on the value indicative of variation and the value indicative of temperature.
 12. The electrosurgical system of claim 11 wherein when the processor determines the presence of the wand condition, the program causes the processor to determine the wand condition as present when the value indicative of variation is below a predetermined value and the value indicative of temperature is at least one selected from the group consisting of: below a predetermined threshold temperature; above the predetermined threshold temperature with the temperature trending toward the predetermined threshold temperature; trending downward; has or exceeds a predetermined rate of change.
 13. The electrosurgical system of claim 11 further comprising: wherein when the processor calculates the value indicative of variation, the program further causes the processor to calculate a value indicative of variation and an average temperature for each of a plurality of calculation windows, the plurality of calculation windows residing within the predetermined period of use; and wherein when the processor determines the presence of the wand condition, the program causes the processor to determine the wand condition as present when the value indicative of variation for each of the plurality of calculation windows is below a predetermined value and the average temperature for each of the plurality of calculation windows is at least one selected from the group consisting of: below a predetermined threshold temperature; above the predetermined threshold temperature with the temperature trending toward the predetermined threshold temperature; trending downward; has or exceeds a predetermined rate of change.
 14. The system of claim 1 wherein the memory stores a program that, when executed by the processor, causes the processor to: calculate a value indicative of variation of the electrical parameter over at least a portion of a predetermined period of use; and determine that a fluid flow through the electrosurgical wand is at least partially blocked based on the value indicative of variation of the electrical parameter.
 15. An electrosurgical system comprising: a processor; a memory coupled to the processor; a voltage generator communicatively coupled to the processor; a temperature sensor, communicatively coupled to the processor; wherein the memory stores a program that, when executed by the processor, causes the system to: supply energy from the voltage generator to an active electrode of an electrosurgical wand; monitor an electrical parameter associated with the energy; receive a value indicative of temperature of a fluid drawn through the electrosurgical wand from the temperature sensor, the receiving over a predetermined period of use and determine, based on the electrical parameter and the value indicative of temperature, the presence of a wand condition of the electrosurgical wand, the wand condition being at least one selected from the group consisting of: a surface area of the active electrode is less than a predetermined threshold surface area; and the surface area of the active electrode is approaching the predetermined threshold surface area; and that a fluid flow through the electrosurgical wand is at least partially blocked.
 16. An electrosurgical system comprising: a processor; a memory coupled to the processor; a voltage generator communicatively coupled to the processor; wherein the memory stores a program that, when executed by the processor, causes the system to: supply energy from the voltage generator to an active electrode of an electrosurgical wand; monitor an electrical parameter associated with the energy; calculate a value indicative of variation of the electrical parameter over at least a portion of a predetermined period of use; and determine, based on the value indicative of variation of the electrical parameter, the presence of a wand condition of the electrosurgical wand, the wand condition being at least one selected from the group consisting of: a surface area of the active electrode is less than a predetermined threshold surface area; and the surface area of the active electrode is approaching the predetermined threshold surface area; and that a fluid flow through the electrosurgical wand is at least partially blocked. 